McLaren is currently using Honda engines in the 2015 Formula One championship. They have a contract to provide engine units for the next ten years to the pinnacle of racing events.
So far, the union has not been successful and has not lived up to the hype created. Honda and McLaren have worked together previously as well and were extremely successful then.
The Honda powertrain has not been the most reliable and is increasing frustration between two former World Champions. Jenson Button and Fernando Alonso have displayed their displeasure openly.
Currently very few manufacturers exist in Formula One - they are Ferrari, Mercedes, Renault and Honda. Out of them Mercedes has done an excellent job with their turbo engine, which is paying dividends now.
Honda begun development of its Formula One engine two years ago and have not been able to extract a winning combination. Restricted budgets and no development during the season are not helping the move ahead.
With ten races done so far in 2015 F1 championship McLaren Honda have secured only 17 points, most of which came from the Hungarian GP where Alonso drove to a fifth place finish.
Red Bull has also warned its manufacturer to act fast as the competition is running far ahead. They too are looking at switching manufacturers for the coming season. McLaren and Honda too are not seeing eye to eye and an early departure would surely be saddening.